瘤野螟咬食誘導水稻蔗糖轉運蛋白OsSUT4基因表現之調控

Abstract

植物在生長發育過程中易發生機械性傷害及蟲害，而植物在受到傷害刺激後會引發一連串生理及代謝反應進行防禦或修護。蔗糖是光合作用之主要產物，參與在植物許多代謝路徑中，且醣類在植物受傷害刺激時具有訊息傳遞功能。瘤野螟 [Cnaphalocrocis medinalis (Guenée)] 為水稻主要啃咬型害蟲之一，其習性為捲葉並啃食上表皮及葉肉。本研究利用瘤野螟四齡幼蟲進行試驗，發現受蟲咬的葉片蔗糖含量會降低；正在發育的未完全展開葉蔗糖含量則會增加，推測水稻植株在瘤野螟咬食後會傾向將蔗糖從受傷部位轉移到正在發育的部位。蔗糖轉運蛋白 (sucrose transporter, SUT) 為植株中負責將蔗糖裝載及卸載於韌皮部的主要蛋白，以助蔗糖於不同器官間進行長距離運輸。水稻SUT基因家族中之OsSUT4基因表現量會受到瘤野螟侵咬刺激而明顯提升，瘤野螟咬食後植株不同葉位OsSUT4不會有系統型的反應，但根部OsSUT4表現將下降。進一步利用訊息傳導因子相關基因及生合成抑制劑探討此誘導表現的機制，發現茉莉酸 (jasmonic acid, JA)、水楊酸 (salicylic acid, SA)、離層酸 (abscisic acid, ABA)、乙烯 (ethylene) 會受到蟲咬刺激而產生，且在傷口處會有過氧化氫 (hydrogen peroxide, H2O2) 的累積。而以茉莉酸、離層酸及過氧化氫生合成抑制劑處理後會降低蟲咬誘導OsSUT4基因表現之反應，顯示這些因子會參與在蟲咬誘導OsSUT4基因表現的路徑中。

Plants were often suffered from many biotic and abiotic stresses such as mechanical wounding and insect herbivores. Plants protect themselves by several defense responses. Sucrose is the major product of photosynthesis. It is involved in many metabolic regulatory pathways and plays an important role in the plant defense responses as signaling molecule. Rice leaffolder [Cnaphalocrocis medinalis (Guenée)] is one of chewing insects. It attacks rice plants by folding leaves and scraping the mesophyll tissues. In this study, we found that after fourth-instar larvae feeding, sucrose contents were decreased in the leaf damaged by leaffolder but increased in developing leaf. Thus, it was suggested that sucrose translocation from damaged leaf to developing sink tissues may be promoted in leaffolder-attacked rice plants. Sucrose transporters (SUT) is the key factor in charge of sucrose loading and unloading in phloem for long-distance translocation in plants. Gene expressions of OsSUT4, a rice SUT gene family member, were significantly induced in leaffolder infestated leaves, but the changes of transcript levels in other leaves were not significant. Rice leaffolder infestation induced jasmonic acid, salicylic acid, abscisic acid and ethylene biosynthesis gene expressions in rice seedlings. Hydrogen peroxide were also accumulated in wounded leaves. Furthermore, leaffolder-induced OsSUT4 gene expressions in leaf tissues would be repressed by inhibitors of jasmonic acid, abscisic acid and hydrogen peroxide biosynthesis. Taken together, the aforementioned results suggested that OsSUT4 gene expression induced by leaffolder infestation was mediated jasmonic acid, abscisic acid or hydrogen peroxide as signalings.